A 27/22 would firm up the body roll tendency but would "increase the understeer" even more than what you have now on the stock '96 thru '99 M3! The reason for this is 27mm would increase the front's stiffness by 90% but the 22mm would increase the rear's stiffness by "only" 46%...giving you even "more" understeer than you had before!

A 26/24 would not only firm up the body roll tendency (front and rear) but also get rid of the understeer...which is what you want.

26/24 is ideal to accomplish both...less roll and get rid of the understeer.